Background: To investigate whether the variation in phenotypic traits of the long-tailed dwarf hamster (Cricetulus longicaudatus) across different environments in Shanxi province conforms to Bergmann&rsquo;s rule. This study collected C. longicaudatus from 9 regions in Shanxi province, namely, Kelan county, Wutai county, Wuzhai county, Qin county, Shanyin county, Xi county, Lingchuan county, Loufan county and Zuoquan county. 
 
Methods: We analyzed the differences in body and skull indicators of C. longicaudatus in different regions and combined environmental factors to explore whether these indicators conform to Bergmann&rsquo;s rule. 
 
Result: Significant inter-population differences were found in multiple phenotypic traits. Hierarchical clustering divided the nine populations into two groups: Group I (Zuoquan, Qin, Wutai, Lingchuan, Shanyin) and Group II (Loufan, Kelan, Wuzhai, Xi). Correlation analysis with environmental factors confirmed that phenotypic variation conformed to Bergmann&rsquo;s rule, indicating geographic differentiation in C. longicaudatus across Shanxi. 
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Bergmann’s Rule Examination based on the Morphology of the Long-tailed Dwarf Hamster (Cricetulus longicaudatus)